1. Field of the Invention
The present invention relates to an OLED display, and more particularly to an OLED display with a current stabilizing device and its driving method.
2. Description of the Prior Art
OLED (Organic Light Emitting Diode) is current-driven device and its luminance is determined by the current intensity. Different levels of luminance (also called gray scale value) can be achieved by controlling the driving current of the OLED, therefore, the current stability is very important. Current uniformity problem will be caused if it fails to provide the OLED with stable current, which will further cause non-uniform illumination.
Referring to FIG. 1, which is a circuit block diagram of a conventional OLED, the conventional OLED comprises an OLED panel 11, a data driver 12 and a scan driver 13. The OLED panel 11 comprises y×x OLEDs 111, wherein the y and x are positive integers. The data driver 12 outputs a Y number of data current I1˜Iy to the y rows (in the vertical direction) of OLEDs 111 via the output circuit (not shown), and then the x rows (in the horizontal direction) of OLEDs 111 produce a image-displaying light source needed by the OLED panel 11 based on the data current I1˜Iy and the scan signals Com1˜Comx outputted by the scan driver 13.
However, in the data driver 12, the power-supply circuit provides constant current I, and a y number of mirror circuits produce data current I1, I2, . . . Iy by multiple mirror reflection. In this case, the data power cables 121 usually should be very long, however, the fact that the data power cables 121 are excessively-long and different in length is an important factor causing uneven current intensities of the data current I1˜Iy.
Furthermore, after the OLED panel 11 is used for a certain period of time, its OLEDs 111 will be deteriorated, which causes internal resistance increase and driving voltage decrease, and as a result, the luminance of the OLED panel 11 will deteriorate in a short length of time (approximately 2 years). As shown in FIG. 2, the curve indicates the reliability changes when the OLEDs are used in a high temperature and humidity environment, wherein internal resistance of the OLEDs increases and the luminance thereof linearly attenuates, namely, luminance decay by 50% (T50) from the initial luminance, which shortens the lifetime of the OLEDs. The phase indicated by the arrow is kind of a running-in period, which means that when the OLEDs are turned on for the first time, their initial luminance will gradually increase during this running-in period and then become constant. However, the curve climbs in the initial phase and then starts declining for the same reason as above. To resolve the problem of the running-in period, the OLEDs should usually be turned on until they become stabilized before being made into final products, which, however, shortens the lifetime of the OLEDs. Without the running-in period, the OLEDs will have the afterimage problem, for example, an initial content (such as ABC) displayed in an initial phase will remain in the full screen phrase, because the OLEDs constituting the initial content ABC are much brighter than those which are turned on afterwards.
The present invention has arisen to mitigate and/or obviate the afore-described disadvantages.